(a) Technical Field
The present disclosure relates to a manufacturing method of a membrane electrode assembly (MEA) for a fuel cell, and more particularly to a method of manufacturing an MEA for a fuel cell which increases performance and durability of an MEA and ensures productivity of the MEA.
(b) Background Art
In general, the membrane electrode assembly (MEA) of fuel cells is composed of two electrodes (i.e., an anode and cathode) and an electrolyte membrane. In general, it is understood by those skilled in the art that the better the bonding at the interfaces between the electrolyte membrane and each of the electrodes, the higher the performance and the durability in most cases.
Conventionally, electrodes (i.e., the catalyst layer) are formed by coating, spraying, or painting catalyst slurry onto a gas diffusion layer, and then heat-compressing the electrodes with a polymer electrolyte membrane, a by coating, spraying, or painting catalyst slurry directly onto a polymer electrolyte membrane, and/or by coating, spraying, or painting catalyst slurry onto a release paper, and then heat-compressing the release paper having the electrodes with a polymer electrolyte membrane and removing the release paper.
As in the method described first above, manufacturing electrodes (catalyst layer) by coating catalyst slurry on a gas diffusion layer is advantageous in forming of pores in the electrodes. However, this manufacturing process is inconvenient to execute, so this process is not used in the manufacture of membrane electrode assembly typically.
Furthermore, in the second method, when electrodes (catalyst layer) are formed directly on a polymer electrolyte membrane, it is possible to manufacture small electrodes, but it is difficult to manufacture electrodes with large areas due to the amount of deformation of the polymer electrolyte membrane that occurs on the larger scales.
However, by coating a catalytic layer (electrodes) on a release paper and transferring the release paper (release paper coated with the catalytic layer) to a polymer electrolyte membrane, electrodes can be easily coated in desired shapes on a release paper and mass production is possible.
There are also many methods of coating a release paper with electrodes. For example, some of these methods include bar coating, comma coating, slot die coating, gravure coating, and spray coating.
Bar coating and spray coating, which are method used for manufacturing a small number of electrodes, are difficult to use for mass production processes. As such, these methods are only used by smaller industry. Comma coating and gravure coating are also difficult to use for mass production processes because they are difficult to control the dimensions of electrodes and the property of the catalyst slurry easily changes.
Slot die coating, however, easily controls the dimension of electrodes and maintains the properties of catalyst slurry because the catalyst slurry is coated in a closed-loop system. Additionally, in this process, the process can continuously coat electrodes having the same dimensions while coating electrodes (catalyst layer) in predetermined directions.
Two currently, known methods of transferring electrodes coated on a release paper to an electrolyte membrane are plate hot pressing and roll pressing. Plate hot pressing transfers electrodes onto an electrolyte membrane generally by pressing them at a temperature of 100° C.-200° C. under a pressure of 5˜50 kgf/cm2 for 1˜10 minutes.
FIG. 1 shows an electrode-membrane bonding process in plate pressing that transfers electrodes coated on release papers to an electrolyte membrane. As shown in FIG. 1, plate pressing transfers two electrodes 4 and 5 coated on release papers 2 and 3, respectively, in a hot press 1 to both sides an electrolyte membrane 6 by pressing the electrodes 4 and 5 with the electrolyte membrane 6 therebetween.
In plate pressing, however, although the interfacial adhesion is sufficient between the electrodes and the electrolyte membrane, the processing speed is slow and mass production is difficult because it takes to long to press the electrodes and an electrolyte membrane for manufacturing a single membrane electrode assembly.
Roll pressing, on the other hand, transfers electrodes onto an electrolyte membrane by heat-compressing them at a temperature of 80° C.-200° C. at a speed of 0.1˜2.0 m/min under a pressure of 1˜40 kgf/cm2. FIG. 2 shows roll pressing that can continuously perform electrode-membrane bonding, with electrodes, which are continuously coated on release papers, by being put in a roll pressing apparatus. As shown in FIG. 2, according to roll pressing, it is possible to continuously manufacture membrane electrode assemblies 16 by continuously transferring electrodes 11 and 13 to electrolyte membranes 15 by bonding release papers 12 and 14 coated with the electrodes 11 and 13 and the electrolyte membranes 15 through a roll press 110.
Although roll pressing in that mass production is easy, the interfacial adhesion is not sufficient between the electrodes and the electrolyte membranes, the continuous bonding process for electrode membrane assemblies does not provide for sufficient adhesion during the high speed process.
In most electrode membrane assemblies, the better the bonding at the interfaces between the electrolyte membrane and each of the electrodes, the higher the performance and the durability. However, when there is separation at the interfaces between the electrodes and the membrane, the performance is reduced, and the separation increases therebetween when the assemblies are operated for a long period of time. As a result, the entire performance of the system rapidly reduces.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.